The present invention relates to devices employed in reinforcement and support of rock structures, and more specifically to nuts having frangible portions for applying tension to threaded rods or bolts which are anchored in blind drill holes in rock formations such as mine roofs, and the like.
Among the means for effecting rock structure support and reinforcement are those wherein an elongated rod or bolt is installed in a blind drill hole bored in the formation. A breakable cartridge containing mutually isolated components of a resin grouting material is inserted into the hole, followed by one end of the rod. The cartridge is fractured against the end of the hole by advance of the rod, and the released resin components are mixed by rotation of the rod. A short time, e.g., a few seconds, after mixing the components harden to provide a secure anchor for the end of the rod within the drill hole.
In the usual situation, it is desirable to place the rod in tension in order to compress and reinforce the rock structure surrounding the drill hole. This may be done by threading a nut on the end of the rod outside the drill hole and rotating nut against a metal support or bearing plate. In order to permit mixing of the resin components and tensioning of the rod in a single operation, nuts have been provided with frangible portions so that the rod will rotate to mix the components in response to rotation of the nut, and the frangible portion will break upon application of excess torque to the nut after sufficient hardening of the grouting mix to apply the desired degree of tension to the rod.
Examples of so-called tension nuts which have been used in the past are shown and described later herein. The frangible portion of some nuts of this type is located in the threaded portion of the nut, raising the possibility that the threads may become fouled or damaged, resulting in malfunction or at least inconsistent operation of such nuts. In other types of tension nuts, the frangible portion may break before the resin components are thoroughly mixed, resulting in poor anchoring of the rod.
It is a principal object of the present invention to provide a novel and improved tension nut for use with a threaded rod in rock support and reinforcement applications.
Another object is to provide a mine roof bolt tension nut which ensures complete and thorough mixing of relatively large amounts of resin grouting components by rotation of an elongated rod upon which the nut is mounted.
A further object is to provide a nut having a frangible portion for fracture by a rod upon which the nut is threadedly secured by application of relatively high torque to the nut, and wherein the fracturing torque is relatively consistent from one nut to the next.
Other objects will in part be obvious and will in part appear hereinafter.